Electron emitting device, electron emitting apparatus and electron beam drawing apparatus

Abstract

An electron emitting device is provided for use in a flat display, an electron beam drawing apparatus, a CRT display and so on. The electron emitting device comprises a first layer having a first bandgap, a second layer formed on the first layer and having the first bandgap, a third layer formed on the second layer and having a second bandgap, which is narrower than the first bandgap, and a fourth layer formed on the third layer and having an electron emitting surface. According to this structure, a high electron emission efficiency can be obtained.

What is claimed is: 
     
       1. An electron emitting device, comprising: a first semiconductor region having a first bandgap;   a second semiconductor region for injecting electrons into said first semiconductor region, said second semiconductor region having a different conductivity type from said first semiconductor region and having said first bandgap disposed on said first semiconductor region;   a third semiconductor region having the same conductivity type as said second semiconductor region and having a second bandgap disposed on said second semiconductor region, said second bandgap being narrower than said first bandgap; and   a fourth semiconductor region having an electron emitting surface disposed on said third semiconductor region.   
     
     
       2. An electron emitting device according to claim 1, wherein a combination of said first material and said second material is selected from the group consisting of one of the following combinations: Al x  Ga.sub.(1-x) As (0≦x≦1) and GaAs; Al x  Ga.sub.(1-x) P (0≦x≦1) and Si; GaAs and Ge; Si and Ge; InAs and GaSb; ZnSe and GaAs; ZnSe and Ge; and CdS and InP. 
     
     
       3. An electron emitting device according to claim 1, wherein said second and third semiconductor regions form a heterojunction. 
     
     
       4. An electron emitting device according to claim 1, further comprising a fifth layer comprising a third material having a low work function disposed on said electron emitting surface. 
     
     
       5. An electron emitting device according to claim 1, further comprising: a first region disposed in at least one of said second semiconductor region and said third semiconductor region; and   a second region disposed surrounding said first region, wherein said first region has a higher carrier density than that of said second region.   
     
     
       6. An electron emitting device, comprising: a first semiconductor region having a first bandgap;   a second semiconductor region for injecting electrons into said first semiconductor region, said second semiconductor region having a different conductivity type from said first semiconductor region and having said first bandgap disposed on said first semiconductor region;   a third semiconductor region having the same conductivity type as said second semiconductor region and having a second bandgap disposed on said second semiconductor region, said second bandgap being narrower than the first bandgap;   a fourth semiconductor region having an electron emitting surface disposed on said third semiconductor region; and   means for applying a bias voltage to said second, third and fourth semiconductor regions.   
     
     
       7. An electron emitting device having a transistor structure, comprising: an emitter;   a base region;   a collector region having an electron emitting region;   means for applying a reverse bias voltage between said base region and said collector region; and   means for applying a bias voltage between said base region and said emitter region,   wherein said base region comprises a first base portion having a first bandgap, and a second base portion having a second bandgap narrower than said first bandgap, and   wherein said first base portion and said second base portion from a heterojunction.   
     
     
       8. An electron emitting device according to claim 7, wherein the combination of said first material and said second material is selected from the group consisting of one of the following combinations: Al x  Ga.sub.(1-x) As (0≦x≦1) and GaAs; Al x  Ga.sub.(1-x) P (0≦x≦1) and Si; GaAs and Ge; Si and Ge; InAs and GaSb; ZnSe and GaAs; ZnSe and Ge; and CdS and InP. 
     
     
       9. An electron emitting device according to claim 7, further comprising a low work function layer comprising a low work function material disposed on said electron emitting layer. 
     
     
       10. An electron emitting device according to claim 7, further comprising: a first region disposed in said base layer; and   a second region surrounding said first region,   wherein said first region has a higher carrier density than that of said second region.   
     
     
       11. A display apparatus, comprising: an electron emitting device comprising a first semiconductor region having a first bandgap, a second semiconductor region for injecting electrons into the first semiconductor region, said second semiconductor region having a different conductivity type from said first semiconductor region and having said first bandgap disposed on said first semiconductor region, a third semiconductor region having the same conductivity type as said second semiconductor region and having a second bandgap disposed on said second semiconductor region, said second bandgap being narrower than said first bandgap, and a fourth semiconductor region having an electron emitting surface disposed on said third semiconductor region;   deflecting means for determining the direction of movement of electrons emitted from said electron emitting device; and   a fluorescent substance being disposed in the direction of movement of said electrons.   
     
     
       12. An electron emitting apparatus including a plurality of electron emitting devices arranged in a matrix on a substrate, said electron emitting devices each comprising: a first semiconductor region having a first bandgap;   a second semiconductor region for injecting electrons into said first semiconductor region, said second semiconductor region having a different conductivity type from said first semiconductor region and having said first bandgap disposed on said first semiconductor region;   a third semiconductor region having the same conductivity type as said second semiconductor region and having a second bandgap disposed on said second semiconductor region, the second bandgap being narrower than the first bandgap; and   a fourth semiconductor region having an electron emitting surface disposed on said third semiconductor region.   
     
     
       13. A display apparatus, comprising: an electron emitting apparatus including a plurality of electron emitting devices arranged in a matrix on a substrate, said electron emitting devices each comprising a first semiconductor region having a first bandgap, a second semiconductor region for injecting electrons into said first semiconductor region, said second semiconductor region having a different conductivity type from said first semiconductor region and having said first bandgap disposed on said first semiconductor region, a third semiconductor region having the same conductivity type as said second semiconductor region and having a second bandgap disposed on said second semiconductor region, the second bandgap being narrower than said first bandgap, and a fourth semiconductor region having an electron emitting surface disposed on said third semiconductor region;   an image signal generator;   X and Y address means for determining the direction of movement of electrons emitted from said electron emitting apparatus; and   a fluorescent substance being disposed in the direction of movement of said electrons.   
     
     
       14. An electron beam drawing apparatus, comprising: an electron emitting apparatus including a plurality of electron emitting devices arranged in a matrix on a substrate, said electron emitting devices each comprising a first semiconductor region having a first bandgap, a second semiconductor region for injecting electrons into said first semiconductor region, said second semiconductor region having a different conductivity type from said first semiconductor region and having said first bandgap disposed on said first semiconductor region, a third semiconductor region having the same conductivity type as said second semiconductor region and having a second bandgap disposed on said second semiconductor region, said second bandgap being narrower than said first bandgap, and a fourth semiconductor region having an electron emitting surface disposed on said third semiconductor region;   means for focusing electrons emitted by said electron emitting apparatus; and   means for controlling a first period of time when said electron emitting apparatus emits the electrons in accordance with said focusing means and for controlling a second period of time when said electron emitting apparatus is prohibited from emitting the electrons.